Hydraulic rotational motors of cam ring type are previously known, comprising a fixed hub-like cylinder housing with a number of peripherally spaced radially oriented cylinders, in which cam roller supporting pistons, usually working diametrically in pairs, act with their radially guided cam rollers against a radially inwardly facing wave-shaped cam curve of a ring element surrounding the cylinder housing. As the piston moves outwards, the rollers are pressed against the cam curve and force it to rotate by virtue of the tangential force created. Characteristic of such hydraulic motors is that they can generate a very high constant torque over the entire rpm range from standing still up to maximum rpm. This type of hydraulic motor therefore has very good starting and low rpm performance without requiring any gears, at the same time as its design is relatively compact, simple and easy to service with the possibility of stepless rotational speed control.
By virtue of these advantageous features, hydraulic motors of cam ring type have found wide-spread application in the operation of relatively heavy industrial units, viz as motors for winches, apron conveyors, mills, drying drums and the like.
For operating units with very large dimensions, such as ore mills, drying ovens, barking drums and the like, today's hydraulic motors of cam ring type have, however, certain limitations.